Aluminum alloy products and surface treatment

ABSTRACT

An aluminum alloy containing 0.05 to 0.15% copper, 0.5 to 0.7% iron, 0.15 to 0.3% silicon, 0.3 to 0.6% manganese, the balance essentially aluminum when properly anodized acquires an attractive integral beige color. Sheet products fashioned from this material are useful in architectural applications such as covering the exterior of large buildings.

United States Patent [191 Anderson et al.

[11] 3,818,566 June 25, 1974 ALUMINUM ALLOY PRODUCTS AND SURFACE TREATMENT Inventors: William A. Anderson; Edmund C.

Franz, both of Pittsburgh, Pa.

Assignee: Aluminum Company of America,

Pittsburgh, Pa.

Filed: June 19, 1972 Appl. No.: 263,767

Related US. Application Data Division of Ser. No. 37,339, May 14, 1970, abandoned.

US. Cl 29/195, 204/58, 204/35 N, 148/6, l48/6.l

Int. Cl C23b 9/02 Field of Search 204/58, 35 N; 29/ I95; l48/6.1, 6

References Cited UNITED STATES PATENTS l/l966 Kampert 204/58 OTHER PUBLICATIONS Appearence Control of Architectural Anodized Finishes by Buskey et al., Kaiser Aluminum & Chemical Corp., 1968, pgs. 6-7.

Primary Examiner-Howard S. Williams Assistant Examiner-R. L. Andrews Attorney, Agent, or Firm-Carl R. Lippert [57] ABSTRACT 8 Claims, No Drawings This is a division of application Ser. No. 37,339, filed May 14, 1970, and now abandoned.

This invention relates to aluminum alloy products, especially sheet products, which can develop unique color response when properly anodized. Especially unique is the ability to develop a very pleasing beige tone which is quite attractive.

Aluminum alloys have found wide acceptance in architectural applications because of their durability and attractiveness together with the ease with which a building can be covered, trimmed or decorated with such. One popular practice contemplates employing an alloy which, upon anodic oxidation of the surface, yields a colored oxide coating. This practice offers advantages in ease of application and color durability. However, the variety of these integral colors together with the uniformity of a given color has been limited. In architectural applications the anodic coating should be about 0.7 mil (0.0007 inch) and often more in thickness so as to provide a sufficiently durable oxide coating. ln coatings of this thickness present technology readily enables achieving rich or dark colors. For instance, shades of gold, bronze, gray and even black are achieved without great effort. However, the delicate or subtle colors and shades are quite elusive especially in the thick architectural coatings.

In accordance with the invention a special alloy composition is provided which, when properly anodized, provides an integral beige colored oxide coating which is quite delicate and exhibits an attractive metallic hue. The beige color is extremely attractive when viewed in the form of a large surface such as would appear on a large building. In addition to the ability to develop the beige color, the improved material can also develop the richer bronze or black colors thus making it a multipurpose alloy which can relieve fabricators of the burden of stocking large numbers of alloy materials. Another advantage of the improved material is its ease of fabrication. It can be readily rolled as a sheet product. It can also be applied as a cladding to a sheet core material. In addition, it can be extruded, forged or otherwise worked into a desired product.

' The improved alloy consists essentially of, by weight, 0.05 to 0.15 percent Cu, 0.5 to 0.7 percent Fe, 0.15 to 0.3 percent Si, 0.3 to 0.6 percent Mn, the balance being aluminum and incidental elements and impurities. A preferred composition contains 0.35 to 0.5 percent Mn. The alloy may include small amounts of incidental elements such as up to 0.01 percent B and 0.05 percent Ti which may be added in casting for grain refining purposes. The alloy may also contain the usual impurities associated with aluminum. Zinc is an innocuous impurity and can be present up to about 0.5 percent.

Fabricating products of the improved aluminum alloy involves no particular problems. In fact, the alloy is especially easy to roll, extrude or otherwise shape into an article. Typically the alloy is cast as by continuous casting to provide stock for the subsequent fabrication procedures. This stock is homogenized by heating to a temperature of at least 950F for a period of time sufficient to dissolve the soluble constituents. a typical time being 24 hours. At this point the stock is hot rolled to provide a plate-like product. Some reheating may be employed if necessary or convenient. The plate is then cold rolled to produce a sheet product having moderate strength. Ease of fabrication is an attractive feature of the present invention in that rolling and other fabrication problems are minimized. The material may be fabricated using essentially the same practices as those used in producing the economical strain hardening aluminum alloys known commercially as l l00 and 3003.

The strength of the alloy is not especially striking. Cold rolled sheet typically exhibits tensile property levels of 15 to 30 ksi. While this strength level is not very high it is adequate for architectural applications such .as curtain walls for large buildings.

If desired, the improved alloy can be provided as a cladding on a core layer of a different alloy. This practice is common in several applications where the strength or some other desirable quality of a core material can be utilized while still obtaining the advantages in appearance, corrosion protection, etc., of a given clad material. Accordingly, the improved material can be hot roll bonded to a core material to provide a laminate plate which is then fabricated into sheet as described above. A typical core material might be alloy 3003 which contains, nominally, 1.2 percent Mn, 0.12 percent Cu, with the balance aluminum and impurities. Other core materials may also be employed where they offer special advantages.

While the above discussion re fabrication is set forth with particular reference to sheet products, such is not intended necessarily to restrict the scope of the invention which should be applicable to extrusions, forgings, and other products. The sheet product, however, is considered preferred since it is in large surfaces that the attractive beige color property is most readily appreciated and accordingly most useful. The sheet products referred to most often range from 0.025 inch to about 0.200 inch in thickness for application in the architectural field. However, thicker or thinner members are also intended to be embraced when referring to sheet and it is not intended to limit such to any arbitrary numerical definition such as is often associated with differentiations between plate and sheet.

If desired, the improved sheet or other product can be annealed, stabilized or otherwise thermally treated without impairing its color response to the subsequent anodic coating application. For instance, if the improved alloy is applied as a cladding on a heat treatable core the composite can be heat treated to develop the properties in the core. This, itself, is significant since many previous alloys are sensitive to thermal treatment in their color response.

The alloy product is next anodized to develop an integrally bonded oxide coating using acidic electrolytes of the type generally known in the anodizing art. Several sheets of the improved alloy containing about 0.] percent Cu, 0.6 percent Fe, 0.2 percent Si and 0.4 percent Mn approximately 0.08 inch in thickness have been anodically anodized in an aqueous bath containing about 15 percent sulfuric acid. The bath is maintained at F and the anodizing is performed at a constant current density of 24 amperes per square foot for a period of time of about 33 minutes. This produces an oxide coating ranging from about 1.0 mil in thickness. V

The coating exhibits an integral beige color with a metallic luster. Perhaps the best way to describe the color is to refer to the Munsell value which is a recognized system of color description which is described in ASTM Designation: Dl535-68; ASTM STANDARDS PART II 1969 p. 285. The Munsell values for this beige color were approximately Y for hue, 7.05 for value and 0.90 for chroma. The beige color can be varied from this level as by increasing the Mn content slightly or altering the anodizing conditions whereby the temperature is lowered and time increased to develop richer colors. Reversing these results in a move toward pale colors. Within these general guide lines the beige color for the improved alloy can be varied such that typical Munsell values would range between 2Y to 8Y for hue, 6.5 to 7.2 for value and /0.65 to H2 for chroma for lighter to darker beige tones. Typical coating thickness can be 1 to L2 mil and still exhibit the delicate beige color. The anodizing conditions can be varied fairly widely. The aqueous bath can contain 130 to 200 grams per liter H 50 The temperature may vary from 70 to 90F and the current density can vary from 6 to 36 amperes per square foot. The time can vary from about 20 to 60 minutes and the coating from 0.7 to 1.2 mils in thickness. Within these varying anodizing conditions the improved material can readily develop anodic oxide coatings exhibiting an integral beige color.

It is usually desirable to seal the anodic coating in the conventional manner, for example by immersing in hot (210F) water or other suitable solutions. The coloration and texture developed by the anodic treatment can be modified by treatment of the surface of the metal product prior to anodic oxidation. The surface can be chemically brightened by washing with a solution of phosphoric and nitric acids or electrochemical means. Mechanical treatments such as buffing, polishing, sand blasting, and the like, can also be employed to alter the texture of the surface.

While achieving the beige color is the truely unique feature of the improved material, its usefulness is enhanced by the ability to provide the black and bronze shades. thus making the improved alloy a multipurpose alloy highly useful in the architectural field. It is also quite significant that the improved alloy products when anodized are free from the structural streaking problems which plague so many prior materials. Structural streaking is the unattractive effect which some aluminum alloy materials exhibit in the end product and which may be alleviated by finishing treatments such as etching or chemical brightening followed by anodic treatments.

What is claimed is:

l. A method of producing a product exhibiting a beige color having a metallic luster comprising 1. providing a shaped body composed of an aluminum base alloy consisting essentially of 0.05 to 0. percent Cu, 0.5 to 0.7 percent Fe, 0.15 to 0.3 percent Si, 0.3 to 0.6 percent Mn, the balance being aluminum and incidental elements and impurities, and

2. anodically oxidizing said body in an aqueous electrolyte containing 130 to 200 grams sulfuric acid per liter of solution at a temperature of about to F while maintaining an anode electrode current density of about 6 to 36 amperes per square foot for a period of about 20 to 60 minutes to produce an anodic coating 0.7 to 1.2 mils in thickness and exhibiting said beige color which is integrally developed in said coating.

2. The method according to claim 1 wherein said shaped body is in the form of rolled sheet.

3. In the production of an aluminum architectural shaped body exhibiting an integrally developed anodic oxide coating having a beige color of metallic luster, the improvement wherein said shaped body is provided in an aluminum base alloy consisting essentially of 0.05 to 0.15 percent Cu, 0.5 to 0.7 percent Fe, 0.15 to 0.3 percent Si, 0.3 to 0.6 percent Mn, the balance being aluminum and incidental elements and impurities, said improvement enabling the development of an anodic oxidation coating 1.0 to 1.2 mil in thickness having an integral beige color characterized by Munsell values of 2Y to 8Y for hue, 6.5 to 7.5 for value and /0.65 to 1.2 for chroma.

4. The improvement according to claim 3 wherein said aluminum base alloy contains Mn in amounts of 0.35 to 0.5 percent.

5. In the production of an aluminum architectural sheet product having an integral beige color developed by anodic oxidation in an electrolyte containing to 200 grams sulfuric acid per liter of solution at a temperature of about 70 to 90F while maintaining a current density of about 6 to 36 amperes per square foot for about 20 to 60 minutes, the improvement wherein said sheet product is provided in an alloy consisting essentially of 0.05 to 0. 15 percent Cu, 0.5 to 0.7 percent Fe, 0.l5 to 0.3 percent Si, 0.3 to 0.6 percent Mn, the balance being aluminum and incidental elements and impurities, said improvement enabling the development of an anodic oxidation coating 1.0 to 1.2 mil in thickness having an integral beige color characterized by Munsell values of 2Y to 8Y for hue, 6.5 to 7.5 for value and /0.65 to 1.2 for chroma.

6. The improvement according to claim 5 wherein said defined alloy is present in the form of a cladding metallurgically bonded to a metal core material of a different composition.

7. An architectural sheet product composed of an alloy consisting essentially of 0.05 to 0.15 percent Cu, 0.5 to 0.7 percent Fe, 0. 15 to 0.3 percent Si, 0.3 to 0.6 percent Mn, the balance being aluminum and incidental elements and impurities, said product having an integrally bonded oxide coating 10 to 1.2 mil in thickness and having an integral beige color characterized by Munsell values of 2Y to 8Y for hue, 6.5 to 7.5 for value and /0.65 to 1.2 for chroma.

8. The improved architectural sheet product according to claim 7 wherein said defined alloy is present in the form of a cladding metallurgically bonded to a metal core material of a different composition.

* l l l 

2. The method according to claim 1 wherein said shaped body is in the form of rolled sheet.
 2. anodically oxidizing said body in an aqueous electrolyte containing 130 to 200 grams sulfuric acid per liter of solution at a temperature of about 70* to 90*F while maintaining an anode electrode current density of about 6 to 36 amperes per square foot for a period of about 20 to 60 minutes to produce an anodic coating 0.7 to 1.2 mils in thickness and exhibiting said beige color which is integrally developed in said coating.
 3. In the production of an Aluminum architectural shaped body exhibiting an integrally developed anodic oxide coating having a beige color of metallic luster, the improvement wherein said shaped body is provided in an aluminum base alloy consisting essentially of 0.05 to 0.15 percent Cu, 0.5 to 0.7 percent Fe, 0.15 to 0.3 percent Si, 0.3 to 0.6 percent Mn, the balance being aluminum and incidental elements and impurities, said improvement enabling the development of an anodic oxidation coating 1.0 to 1.2 mil in thickness having an integral beige color characterized by Munsell values of 2Y to 8Y for hue, 6.5 to 7.5 for value and /0.65 to 1.2 for chroma.
 4. The improvement according to claim 3 wherein said aluminum base alloy contains Mn in amounts of 0.35 to 0.5 percent.
 5. In the production of an aluminum architectural sheet product having an integral beige color developed by anodic oxidation in an electrolyte containing 130 to 200 grams sulfuric acid per liter of solution at a temperature of about 70* to 90*F while maintaining a current density of about 6 to 36 amperes per square foot for about 20 to 60 minutes, the improvement wherein said sheet product is provided in an alloy consisting essentially of 0.05 to 0.15 percent Cu, 0.5 to 0.7 percent Fe, 0.15 to 0.3 percent Si, 0.3 to 0.6 percent Mn, the balance being aluminum and incidental elements and impurities, said improvement enabling the development of an anodic oxidation coating 1.0 to 1.2 mil in thickness having an integral beige color characterized by Munsell values of 2Y to 8Y for hue, 6.5 to 7.5 for value and /0.65 to 1.2 for chroma.
 6. The improvement according to claim 5 wherein said defined alloy is present in the form of a cladding metallurgically bonded to a metal core material of a different composition.
 7. An architectural sheet product composed of an alloy consisting essentially of 0.05 to 0.15 percent Cu, 0.5 to 0.7 percent Fe, 0.15 to 0.3 percent Si, 0.3 to 0.6 percent Mn, the balance being aluminum and incidental elements and impurities, said product having an integrally bonded oxide coating 1.0 to 1.2 mil in thickness and having an integral beige color characterized by Munsell values of 2Y to 8Y for hue, 6.5 to 7.5 for value and /0.65 to 1.2 for chroma.
 8. The improved architectural sheet product according to claim 7 wherein said defined alloy is present in the form of a cladding metallurgically bonded to a metal core material of a different composition. 